Gout, a common form of inflammatory arthritis, results from elevated uric acid concentrations in the blood. Recently, genome-wide association studies (GWAS) identified SLC2A9 and ABCG2 genes as major regulators of hyperuricemia along with SLC22A12, SLC17A1, ABRB3 and MTHFR. However, genetic variation in these genes explains only a small proportion of the total variation in serum uric acid in Caucasians. A recent study (Nat Genet. 43:1127-30, 2011) in 6,017 Icelanders identified a rare missense single nucleotide polymorphism (SNP) in the aldehyde dehydrogenase 16A1 (ALDH16A1) gene to be associated with gout (P = 1.5 x 10-16) and serum uric acid levels (P = 4.5 x 10-21). Although this is a rare SNP, its high association is strongly suggestive of a novel ALDH16A1-mediated pathway of regulating uric acid levels. ALDH16A1 is a novel and rather unique member of the ALDH superfamily. All ALDH16 proteins from bacteria to mammals contain two (rather than one) ALDH domains, four transmembrane domains and a coiled-coil domain. Interestingly, mammalian ALDH16 proteins lack the Cys-302 of the active site that is normally necessary for catalytic activity. Our recently published data have confirmed this lack of catalytic activity. Accordingly, any cellular actions of ALDH16A1 are likely to rely on some non- catalytic functionality. An example of this is the interaction of ALDH16A1 with maspardin, a protein associated with Mast syndrome. Molecular modeling and experimental evidence from our laboratory suggests that human ALDH16A1 interacts with hypoxanthine phosphoribosyltransferase 1 (HPRT1), a molecule that plays a key role in the purine salvage pathway and, relatedly, uric acid production. Absence of HPRT1 activity (Lesch-Nyan syndrome) or reduced HPRT1 function (Kelley- Seegmiller syndrome) are known to cause hyperuricemia and gout. Our preliminary studies show that increased cellular ALDH16A1 results in reduced cellular uric acid levels. Based upon these data, our working hypothesis is that ALDH16A1 modulates uric acid levels by enhancing HPRT1 activity through a protein-protein interaction. Dysregulation of the effects of ALDH16A1 could lead to increased serum uric acid levels and contribute to diseases involving hyperuricemia. Accordingly, we propose to: Specific Aim 1. Confirm the protein-protein interactions between human ALDH16A1 and HPRT1 and investigate the biochemical implications of such interactions. Specific Aim 2. Investigate the role of ALDH16A1 in modulating cellular uric acid levels. When completed, the results obtained in the present proposal will lay the groundwork for a more detailed and focused R01 application aimed at thoroughly understanding the role of ALDH16A1 in gout, with the ultimate goal of preventing and treating this debilitating disease.